ELECTRONIC-STRUCTURE AND OPTICAL-RESPONSE IN GAAL1-XN SOLID ALLOYS

A new method for the calculation of the electronic band structure for the GaxAl1-xN solid alloys is proposed. We present the solid alloy str ucture as a superposition of two sublattices with the appropriate weig hting factors. Both the ab initio norm-conserving pseudo-potential (PP ) and LCAO methods give essential disagreement with the experimental d ata. Only the appropriate correction of the norm-conserving PP method by the orthogonalized LCAO wave functions essentially stabilizes the c onvergence procedure. To check the reliability of the proposed method we have carried out experimental investigations of the optical functio ns for two representatives of the investigated wurtzite solid alloys: GaxAl1-xN (x = 0.85 and 0.65). Calculations were performed as a functi on of the energy cutoff as well as of the Slater screening parameter a lpha. The optical functions at zero frequency give overestimated value s compared with the experimental data. The best agreement with experim ent can be achieved by using the orthogonalization procedure between t he norm-conserving PP and LCAO wave functions. The latter ones help in understanding the solid alloy structure modulations in the compounds mentioned. The possibility is shown of achieving good agreement betwee n the experimental and theoretical data. (C) 1998 Elsevier Science B.V .